Food scientists have long been interested in using a wide variety of protein sources to produce food products which resemble meat. Among the most sought for alternatives have been processes for converting protein sources such as oilseed flours, meals, cereal proteins and microbial proteins to more acceptable protein food products particularly those which resemble meat in texture. This impetus has resulted in the development of a wide variety of techniques to produce textured protein food products resembling meat. The most common technique has been the wet spinning process as disclosed in U.S. Pat. No. 2,730,447 to R. A. Boyer. The wet spinning process generally produces protein fibers by extruding a plurality of fine streams of an aqueous solution of protein into an acid chemical coagulating bath. The protein coagulates into fine fibers which are then collected and treated to form an edible textured protein product. Other methods of producing textured protein products resembling meat have included a shred-like protein product formed by heat coagulation of undenatured protein as disclosed in U.S. Pat. No. 3,047,395 to Rusoff et al.
Since development of these early processes for forming textured protein products from a variety of edible protein sources, expanded textured products have been produced by the extrusion of a proteinaceous source through an environment of elevated pressure and temperature into an environment of substantially lower pressure with resultant puffing and expansion of the product. The expanded product has textural characteristics upon rehydration with water which is very similar to a real piece of meat. Extrusion techniques for the production of expanded protein products, especially those derived from oilseed meals are described In U.S. Pat. Nos. 3,488,770 and 3,496,858.
More recently a process for the production of protein filaments from a wide variety of protein sources has been disclosed and provides a method for producing edible protein filaments without a requirement for special equipment, thereby avoiding a large capital expenditure in order to commercialize the process. The noted process has generally involved heating a slurry of proteinaceous material by conducting the slurry through a heat exchanger at a proteinaceous solids level of between about 0.5 and 35% by weight under pressure and heating the slurry in a heat exchanger for sufficient period of time so that elongated filaments are separated from the slurry. The heated slurry is thereafter continuously removed from the heat exchange zone through a back pressure creating orifice whereby discrete elongated filaments are discharged into the collecting zone. The protein filaments which are formed are highly useful in making a wide variety of food products, and may be conveniently incorporated with conventional meat sources to form food products having improved aesthetic appeal, flavor and economy. Processes of the above type which may be included to form these unique, elongated protein filaments include those described in U.S. Pat. Nos. 3,662,671, 3,662,672, 3,821,453 and Re. 28,091 all of which are incorporated herein by reference. These processes have provided an effective solution to the attendant problems associated with prior art processes for the production of textured protein food product from a variety of protein sources. The present invention is specifically intended to comprise an improvement over the processes disclosed in the above identified patents since it has been determined that for certain food applications, specifically those involving addition of the protein filaments to a meat source, it is preferable for the filaments to have a pH above about 6.0 and preferably between about 6.0 and 7.0 since a protein filament having a pH in this range possesses better cooking properties in the meat product as compared to filaments which have a lower pH in the vicinity of 4.5 to 5.5. A higher pH for the protein filaments can obviously be achieved by adjusting the pH of the slurry prior to filament formation to the desired range of about 6.0 and while filaments obtained in this manner are satisfactory, it has been determined that the yield of protein filaments from a given weight of the proteinaceous slurry if the pH is adjusted in this manner is somewhat lower than would be desirable for a commercial process depending on the process conditions employed. Therefore, a need has been created for a more efficient process for the production of a pH modified protein filament having a pH above about 6.0 or within the range of 6.0 to 7.0 without decreasing the yield of the proteinaceous filaments or altering the desirable functional properties thereof. U.S. Pat. No. 3,928,641 herein incorporated by reference describes a method of collecting protein filaments of the above type in which discharge of the filaments from a heat exchange zone into the collecting zone is controlled by confining the stream of filaments exiting the orifice to within a critically defined total angle of between about 4.degree.and 90.degree., said angle being measured in relationship to a theoretical axis through the central portion of the nozzle or back pressure creating orifice. Confinement of the stream of filaments in this manner prevents lumping at the periphery of the collecting zone by fine filaments which can be created by atomization of the slurry. These undesirable lumps of fine filaments can be discharged into the collecting zone and into the final product. The discharge of these filaments is controlled by the use of a shield placed over the nozzle with a conically shaped diverging section having a total angle of between about 4.degree. and 90.degree.. This shield section provides a means of confining the ejected slurry until the filaments are sufficiently cooled that no accumulation of any fine filaments results.
It is, therefore, an object of the present invention to provide a process for the pH modification of protein filaments.
It is a further object of the present invention to provide a process for the pH modification of protein filaments wherein the maximum yield of protein filaments from a given weight of proteinaceous slurry is achieved.
It is also an object of the present invention to provide a process for the pH modification of protein filaments wherein said modified filaments are especially suitable for addition to meat products as an extender.